Urochordata represented by tunicates: Very Smart Mathematical Dog. The tetrapods paleontological record In animal: Its surface is covered with horny material and bears thorn-like projections which carry taste buds and mucous glands. Mouth is terminal, slitlike aperture bounded by horny Jaws.
Mouth is a wide, slit present at the anterior end of head. Mouth is terminal, slitlike aperture bounded by horny Jaws. Mouth is sub-terminal, cleft bounded bv mobile, fleshy lips. Buccal cavity is a narrow gap. Labial glands are present on lips.
Buccal cavity is narrow and some what and dorsoventrally flattened 2. Buccal cavity is a spacious chamber andits space between lips and the teeth is called vestibule. This receives the mouth opening.
On both jaws teet are present, polyphyodont homodont teeth arranged in a single row on each jaw. Teeth are not useful for mastication.
Pleurodont dentition is present. Jaws are modified into tooth less beak. Teeth are diphyodont, heterodont and thecodont.
These are arranged in a single row on each Jaw. Sensory papillae are present. Tongue is narrow triangular and fleshy. Its surface is covered with horny material and bears thorn-like projections which carry taste buds and mucous glands.
Tongue is highly specialized, fleshy and muscular and can be moved in different directions. It can be protruded out. Its surface is rugose being covered with numerous papillae along with taste buds. A pair of internal nostrils open into the roof of the buccal cavity anteriorly. Hard palate is present. A bony palate is wanting in birds but a pair of palatal folds and palatal groove between the two folds are present. Internal nostrils are located dorsal to the palatal folds. The nasal passages are separated from the buccal cavity by a bony palate.
The internal nostrils open into the pharynx nearer to glottis. A bony palate is present covering the roof of the buccal cavity. A bony palate is absent. But soft palate is formed of two membranous folds.
The palate is differentiated into anterior bony hard palate and a soft palate is formed of connective tissue. The soft palate is produced behind into a process — velum palati hanging down from the roof, which prevents the entry of food into nasal passage.
Unicellular mucous glands are present and keep the buccal cavity always wet. Unicellular mucous glands are absent in the epithelium of bucco-pharyngeal region.
Uni cellular mucous glands are absent. But multi cellular serous glands are present. Salivary glands are absent. But labial glands are open at the lips which do not play any role in digestion. Salivary glands which open into the buccal cavity are lingual, mandibular, maxillary, cricoary tenoid, palatinal and sphenopalatinal glands. The multi cellular salaivary glands are four pairs.
They are Infra orbital, parotid, sublingual and sub-maxillary glands. Pharynx is marked off. On the roof of pharynx near the junction of two jaws a pair of openings is called Eustachian apertures.
Pharynx is not sharply demarcated from the buccal cavity. It receives the openings of esophagus and the glottis. Esophagus is a narrow tube and straight extends through the neck. Mucous glands are present. Oesophagus is a bng and narrow tube. It has thick walls. Mucous glands are absent. Oesophagus is a long thin walled tube.
It is clearly marked off from the pharynx as well as stomach. The principal functions of the kidney are the removal of nitrogenous wastes resulting from the oxidation of proteins and the regulation of water loss. Vertebrates eliminate three kinds of nitrogenous wastes: Ammonia and urea are highly soluble in water, but uric acid is not. Ammonia is highly poisonous, urea is slightly poisonous, and uric acid is not poisonous at all.
Among reptiles the form taken by the nitrogenous wastes is closely related to the habits and habitat of the animal. Aquatic reptiles tend to excrete a large proportion of these wastes as ammonia in aqueous solution.
This method uses large amounts of water and is no problem for a freshwater resident, such as an alligator , which eliminates between 40 and 75 percent of its nitrogenous wastes as ammonia.
Terrestrial reptiles, such as most snakes and lizards, must conserve body water, and they convert their nitrogenous wastes to insoluble, harmless uric acid, which forms a more or less solid mass in the cloaca. In snakes and lizards, these wastes are eliminated from the cloaca together with wastes from the digestive system. Prior to the evolution of the metanephric kidney, the products of the male gonad , the testis, traveled through the same duct with the nitrogenous wastes from the kidney.
But with the appearance of the metanephros , the two systems became separated. The female reproductive system never shared a common tube with the kidney. Oviducts in all female vertebrates arise as separate tubes with openings usually near, but not connected to, the ovaries. The oviducts, like the Wolffian ducts of the testes , open to the cloaca.
Both ovaries and testes lie in the body cavity near the kidneys. With the evolution of the reptilian egg , internal fertilization became necessary. The males of all modern reptiles, with the exception of tuatara , have functional copulatory organs.
Unlike the penis of turtles and crocodiles, the copulatory organ of lizards and snakes is paired, with each unit being called a hemipenis. The hemipenes of lizards and snakes are elongated tubular structures lying in the tail. Completion of the erection is brought about by blood filling the sinuses in the erectile tissue. Only one hemipenis is inserted into a female, but which one is a matter of chance. Unlike the penis of mammals, the copulatory organs of reptiles do not transport sperm through a tube.
The ducts from the testes, as already mentioned, empty into the cloaca, and the sperm flow along a groove on the surface of the penis or hemipenis. In general construction the eyes of reptiles are like those of other vertebrates. Accommodation for near vision in all living reptiles except snakes is accomplished by pressure being exerted on the lens by the surrounding muscular ring ciliary body , which thus makes the lens more spherical.
In snakes the same end is achieved by the lens being brought forward. The lens moves as a result of the pressure built up on the vitreous humour by contractions of muscles located at the base of the iris.
The pupil shape varies remarkably among living reptiles, from the round opening characteristic of all turtles and many diurnal lizards and snakes to the vertical slit of crocodiles and nocturnal snakes and the horizontal slits of a few tree snakes.
Undoubtedly the most bizarre pupil shape is that of some geckos , in which the pupil contracts to form a series of pinholes, one above the other. The lower eyelid has the greater range of movement in most reptiles. In crocodiles the upper lid is more mobile.
Snakes have no movable eyelids, their eyes being covered by a fixed transparent scale. Visual acuity varies greatly among living reptiles, being poorest in the burrowing lizards and snakes which often have very small eyes and greatest in active diurnal species which usually have large eyes. Judging by the size of the skull opening in which the eye is situated, similar variation existed among the extinct reptiles. Extinct forms, such as the ichthyosaurs, that hunted active prey had large eyes and presumably excellent vision; many herbivorous types, such as the horned dinosaur Triceratops , had relatively small eyes and weak vision.
Colour vision has been demonstrated in few living reptiles. We welcome suggested improvements to any of our articles. You can make it easier for us to review and, hopefully, publish your contribution by keeping a few points in mind.
Your contribution may be further edited by our staff, and its publication is subject to our final approval. Unfortunately, our editorial approach may not be able to accommodate all contributions. Our editors will review what you've submitted, and if it meets our criteria, we'll add it to the article.
Please note that our editors may make some formatting changes or correct spelling or grammatical errors, and may also contact you if any clarifications are needed.
Digestive and urogenital systems The digestive system of modern reptiles is similar in general plan to that of all higher vertebrates. Sense organs Sight In general construction the eyes of reptiles are like those of other vertebrates.
Previous page Circulatory system. Page 9 of Learn More in these related Britannica articles: Reptile s, of which there are few endemic families, have mainly Old World affinities.